Process control of compacted graphite iron production in pouring furnaces

ABSTRACT

A method for continuously providing pretreated molten iron for casting objects which solidify as compacted cast iron, in which inoculating agents are added immediately prior to casting, in exact quantities. In practicing the method, the ability of the fully treated cast iron to crystallize is measured and the result of this measurement is used for feedback control of the supply of inoculating agent, this supply being effected at the last possible stage of the treatment process, so as to optimize the amount of inoculating agent introduced to the system. Since the inoculating a gent will normally include FeSi, it will also fed back and used to increase or reduce the addition of agents for adjusting the carbon and/or silicon contents of the iron as necessary.

This application claims benefit of international applicationPCT/SE94/01177 filed Dec. 7, 1994.

BACKGROUND OF THE INVENTION

The present invention relates to a method for providing pretreatedmolten iron for casting objects which solidify as compacted graphiteiron.

Compacted graphite iron, below abbrivated as CGI, is a type of cast ironin which graphite appears in a vermicular form (also referred to ascompacted cast iron or vermicular iron) when viewed on a two-dimensionalplane of polish; vermicular graphite is defined as "Form III" graphitein ISO/R 945-1969, and alternatively "Type IV" according to ASTMSpecification A 247.

The mechanical properties of CGI are a combination of the bestproperties of gray iron and ductile iron. The fatigue strength andultimate tensile strength of CGI are comparable with the values forpearlitic ductile iron, while the thermal conductivity of CGI is similarto that of gray iron. In spite of this, CGI presently represents only alimited part of the total world production of cast iron, as comparedwith gray iron which constitutes about 70% of the total cast ironproduction, and ductile iron which constitutes about 25% of totalproduction.

One reason for the prior limited production of CGI is because of thedifficulty and reliably producing it. This difficulty stems from thefact that the graphitization potential and the graphite shape-modifyingelements of the iron must be simultaneously controlled within a verynarrow range during the production process. This has been achievedhitherto with the aid of a large number of tests and experientiallywell-defined and often expensive additions to the system. However,theses difficulties have been removed in the most part by the methodsdescribed in SE-B-444,817, SE-B-469,712 and SE-B-470,091. SE-B-444,817describes a method of producing cast iron which includes graphiteshape-modifying agents, this method being based on a thermal analysiswhich enables the graphite precipitation and growth to be establishedbased upon the actual solidification process of a small andrepresentative sample and to finally treat the melt with additionalgraphite shape-modifying elements as required for optimal solidificationof CGI upon casting. The time-dependant change in temperature in thecenter of a sample and at a point in the melt lying close to the wall ofthe sampling vessel during the solidification process is recorded,whereby two different solidification curves are obtained which can beused to provide information relating to the course of solidification ina casting process. Since this sampling method provides quick and veryprecise information concerning the inherent crystallization propertiesof the melt, the subject matter of SE-B-444,817 represents a firstrealistic possibility of controlling the production of CGI on a largescale.

SE-B-469,712 teaches a development of the method taught by SE-B-444,817,in which there is used a special type of sample container having wallssupplied with a substance which lowers the concentration of elementarymagnesium dissolved in the melt close to the container wall by at least0.003%. This is done to create a margin against such lowering of theMg-content as to result in the formation of flaky graphite; with regardto elementary Mg, the transition from the formation of compactedgraphite to the formation of flaky graphite namely extends over aconcentration range of only 0.003 percentage units, principally from0.008% to 0.005%, although the absolute values may vary depending on thesolidification time.

SE-B-470,091 describes a further development of the method taught bySE-B-444,817. This patent specification describes how it is alsopossible to determine the physical carbon equivalent (C.E.) orgraphitization potential of structurally modified cast iron melts, amongothers CGI which has a C.E.-value higher than the eutectic point. Again,the thermal analysis results are used to correct or regulate thecomposition of the melt. The method is based on introducing into asample vessel pieces of iron of low carbon content, wherein the size ofthe pieces is adapted so that the pieces will not melt completely whenthe vessel is filled with molten iron. The temperature of the melt isrecorded as the melt solidifies. When the temperature crosses theγ-liquidus line, this temperature is recorded as an absolute temperatureor as a temperature difference in relation to the measured andcalibrated values of the eutectic temperature for structurally modifiedcast iron of a similar kind; the C.E. of the melt is determined on thebasis of a phase diagram for this structurally modified cast iron.

The teachings of these patent specifications represent in all essentialsthe state of the art on which the methods of producing CGI of uniformquality on an industrial scale are based. This was scarcely realisticwith the older methods described in, e.g., DE-A1-29,37,321 (Stefanescu),DE-C1-34,12,024 (Lampic) or JP-52,026,039 (Komatsu), as those methodswere heavily laden with scrap problems. However, as mentioned above, theproduction of CGI is still quite modest. One important reason for thisis that it has not been possible hitherto to reliably control theproduction of CGI in any continuous or semi-continuous processes, butonly in batchwise processes.

By "continuous process" is here basically meant a process forcontinuously providing molten iron that solidifies as CGI, for instancefor casting in moulds arranged in a continuously running moulding line,i.e. a process from which an unbroken stream of such molten iron can beobtained continuously without any interruption of the process forfeeding of raw material or removal of treated iron, as distinct from a"batch process", by which is meant production and dispensing ofindividual parcels of molten iron that solidifies as CGI, optionallyfollowed by a subsequent similar batchwise operation; by a"semi-continuous process" is meant an overall process comprising both abatchwise subprocess and a continuous subprocess, e.g. a processinvolving batchwise treatment and feeding of raw material to a reactor,from which the final products could be obtained on a continuous basis,i.e. without any interruption; in the present case, this means that theprocess provides an option to produce a continuous strand of CGI,although it is still possible to produce independent castings of CGI,optionally in a continuously running moulding line.

One important difference between a batch process, on one hand, and acontinuous or a semi-continuous process, on the other hand, is that in abatch process the product properties in principle cannot be changed oradjusted from one produced item to another, but only when a new batch ofmaterial is prepared, while in a process that comprises at least onecontrolled continuous subprocess such changes or adjustments inprinciple can be made at any point in time; in the present case, this iseffected by on-line control of the contents of inoculation agents (andoptionally also of graphite shape modifying agents) in the melt iron atthe latest possible stage of the production process prior to casting, aswill be discussed in more detail later. For the sake of simplicity, andjustified by the difference discussed above, both the concept of"continuous" as well as that of "semi-continuous" processes will in thisdocument be embraced by the term "continuous process".

The fact that in order to be economically rewarding the large scaleproduction of near-net-shape cast metals or alloys will sooner or laterrequire a continuous manufacturing process would be obvious to thoseactive in this field of technology. A continuous process would have anumber of advantages in relation to a batch process, as should be clearto any person skilled in the art. From the aspect of logistics, forinstance, continuous manufacturing processes would be advantageous inthat the potential danger of "congested sections" or "bottlenecks" inthe production chain would be considerably smaller, providing foroptimized economic use of the production plant.

As mentioned in the introduction, one of the major reasons why CGI isstill produced by batch-wise processes rather than by continuousprocesses is because the process control problems of the oldertechniques have not allowed for reliable continuous CGI productionprocesses.

All technical development of any practical significance within thisfield has been directed towards solving the problem of batch-wisemanufacturing processes. The aforesaid patent specifications thusdescribe methods which are directed to controlling and regulating thecomposition of a given melt of limited volume, i.e. a batch. A sample istaken from this batch and if the result of the thermal analysis showsdeviations from specified values, the composition of the entire batch iscorrected, i.e. if such correction is at all possible; if thecomposition of the batch cannot be corrected, the entire batch isdiverted.

Subsequent to taking the sample and correcting the composition of themelt, the molten iron is cast in accordance with known methods asquickly as possible, and normally within 5-20 minutes. Many of theadditives in the melt react chemically and become inactive at liquidiron holding temperatures when the waiting time is too long. Thus, batchproduction process conditions do not allow more than one samplingoccasion with each batch, and are intolerant of process interruptions.The sample is taken from a transfer ladle and the melt shall have timeto be de-slagged and transported to the final treatment station duringthe time of analyzing the sample, wherein the results of the analysisare then used to make any necessary adjustment to the melt prior tocasting. A terminating thermal analysis is unsuitable because this wouldreduce the available casting time. Thus, although advantageous in manyways, the prior art processes would not seem to form a good basis forany continuous manufacturing process, since there are no opportunitiesprovided for on-line control of the product properties according to saidprior art, but only for adjustment of one batch at the time.

During batch production methods, a major quantity of inoculating andgraphite-modifying agents are introduced into the melt at an early stageof the process, whereafter the thermal analysis sampling process iscarried out and corrections are made immediately prior to casting. Thismajor quantity of inoculating agent must be considerably larger than theamount corresponding to the required content in the iron to be cast,since the inoculating agent has a limited effect; the inoculating agentstimulates the formation of graphite crystals, but if casting andtherewith cooling of the melt is not eminent, a number of thecrystallization nuclei thus formed will redissolve in the melt or bephysically removed from the melt by, for example, flotation. It would ofcourse be desirable to reduce the used quantity of inoculating agent toan amount that corresponds to the required content in the iron to becast.

The amount of sulphur present in the cast iron melt introduced into theprocess must be kept at a low level; sulphur per se is undesirable inCGI and therefore must in all events be removed during the course of theprocess. A high S-content will also reduce the accuracy of the thermalanalysis. Any sulphur present will react with Mg, which is the graphiteshape modifying agent commonly used in such processes. As made evidentin SE-B-469,712, only dissolved Mg in elementary form has a graphiteshape-modifying effect. When analyzing the measuring result, a highS-content causes uncertainty as to whether or not the major part of theMg added to the system has reacted completely with the sulphur presentat the time of taking the sample, and therewith uncertainty as to theextent to which the melt needs to be corrected. It would of course bedesirable to find a way to reduce or even remove these uncertainties.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for a continuousmethod of CGI production, having the desirable properties indicatedabove, by means of an improved way of performing process control.

By deviating from the direction in which the prior art has developed andinstead thermally analyzing the fully treated iron, the aforedescribedproblems are overcome and CGI can be produced by a continuous process.

According to the present invention, inoculating agents need only beadded immediately prior to casting, i.e. in exact quantities, which hasnot been possible in conventional methods, where inoculating agent isadded early in the process and then in considerable, but necessaryexcess amounts. In the case of the present invention, however, theability of the fully treated cast iron to crystallize is measured andthe result of this measurement is used for feedback control of thesupply of inoculating agent, this supply being effected at the lastpossible stage of the treatment process, so as to optimize the amount ofinoculating agent introduced to the system. Since the inoculating agentwill normally include FeSi, it will also influence the C.E.-value, andhence the result is also fed back to step II and used to increase orreduce the addition of agents for adjusting the carbon and/or siliconcontents of the iron as necessary.

When practicing the present invention, it is easier to accommodate ironmelts with high S-contents, if such melts have to be used. Adesulphurization step can be provided prior to transferring the moltencast iron into the conditioning furnace, or, as an alternative, a givenquantity of graphite shape modifying agent can be added which, inaddition to the amount required to modify the structural properties,also includes a stoichiometric quantity corresponding to the S-contentof the iron, so that, in principle, all sulphur will have reacted by theend of the process, and so that the resultant CGI will be free fromsulphur in solution. As mentioned in the aforegoing, however, thisreaction is far from being instantaneous and impairs the samples takenduring the course of the process. When practicing the present invention,however, the sample is taken at the end of the process from an iron meltwhich, on average, has been kept for quite a long period of time in theconditioning furnace. With each new batch of melt transferred to theconditioning furnace, the active S-concentation of the respective newbatch is reduced by mixing the batch with melt of lower activeS-concentration present in the conditioning furnace, and the addedsulphur is given time to react more completely prior to taking therespective sample.

The production of molten cast iron in step I is conveniently effected ina melter, for instance a cupola furnace or an electric furnace, and mayconsist of a duplex-process including a melting and a treatment furnace.The raw material used to produce the melt may be iron scrap, virgin ironraw material, foundry returns, or other conventional iron foundry chargematerials, or combinations of these; even though not preferred, the rawmaterial may have a relatively high S-content.

The C.E.-value of the melt is adjusted in step II with the aid of carbonand/or silicon or low carbon iron, which are added in quantitiescorresponding to the result of the thermal analysis of the melt that hasjust been cast; the principle on which the C.E. is adjusted is thusessentially in accordance with the method described in SE-B-470,091.

According to one embodiment of the inventive method, below referred toas embodiment A, the melt is then transferred in to a reaction vessel,normally in the form of a ladle, in which the melt is subjected to abase treatment process in which a graphite shape modifying agent, suchas Mg for instance, is added in an amount governed by the aforesaidanalysis result, essentially in accordance with the methods described inSE-B-444,817 and SE-B-469,712. The Mg can be added to the melt inaccordance with any appropriate conventional method. Mg-containingalloys (e.g. FeSiMg-alloy containing 45-60% Fe, 40-70% Si and 1-12% Mg)can be used in a so-called sandwich-process (i.e. the alloy is placed onthe bottom of the reaction vessel and the melt poured over the alloy),although preferably pure Mg will be added, since this generates lessslag. Pure Mg can be added in wire form for instance, or in a so-calledGF-converter (GF=Georg Fisher AG). As mentioned in the aforegoing, it isnot necessary to include an inoculating agent in the base treatmentprocess, although there is nothing to prevent the basic process fromincluding the addition of an inoculating agent.

Upon completion of the optional base treatment process, the slag isremoved from the melt and the melt is transferred to a conditioningfurnace, which may be an open furnace when, for instance, the processconditions are such that the melt is protected from atmospheric oxygenby a continuous slag layer, although a closed furnace is preferablyused, this furnace being preferably provided with an inert shielding gasatmosphere. This minimizes undesirable oxidation of the meltconstituents, and then particularly readily oxidized graphiteshape-modifying agents such as Mg. When using a shielding gas, the gasused may be any non-oxidizing gas such as nitrogen or a nobel gas, forinstance, or a mixture thereof.

According to one embodiment of the invention, there is used a closedconditioning furnace which is also preferably pressurized. In additionto pressurizing the furnace and therewith further reducing the ingressof air to the melt in the conditioning furnace, when the conditioningfurnace is appropriately constructed the furnace pressure can beregulated so as to control emptying of the melt into casting moulds inan advantageous manner; this will be described in more detail below.

The furnace may, for example, be of the PRESSPOUR type, for instance afurnace of the type sold by the company ABB. The batch charged is mixedin the conditioning furnace together with the existing melt.

The refilling of the melt contents of the furnace is typically up toabout 25%, since this turnover level has been found to provide a goodcontent equalizing effect.

According to embodiment A further graphite shape modifying agent, forinstance Mg, may be added to the melt in the conditioning furnace, if sorequired. The Mg can be supplied in the form of steel-sheathed Mg-coredwire or rod, which is fed into the furnace through a closable opening inthe furnace cover or lid. As with the earlier additions, the amount ofMg added to the system is governed by the result of the thermal analysisof the fully treated CGI either, in or immediately upstream of thecasting mould. There is a danger of gas forming in the melt when atleast certain graphite shape modifying agents are added thereto, such asMg for instance, which readily vaporizes when entering the melt. Whenthe conditioning furnace is pressurized the gas thus generated is liableto disrupt the pressurization control system. Consequently, the pressurein the conditioning furnace is preferably reduced when adding a graphiteshape modifying agent to the melt while in the conditioning furnace.

In another embodiment, below referred to as embodiment B, beingalternative to embodiment A, the molten cast iron is transferred fromthe conditioning furnace to a small pouring ladle before being pouredinto casting moulds, and the total quantity of graphite shape modifyingagent is added into the ladle in accordance with the aforementioned meltregulating principle, i.e. the base iron held in the conditioningfurnace has not previously been treated with magnesium.

The sequence of production steps is terminated by taking a sample forthermal analysis. The sample is preferably taken in a pouring basin orsprue system, although it can also be taken from the casting stream or,for instance, from a pouring ladle, if any. The sample may be takenmanually, for instance with the aid of a hand-held lance, or fullyautomatically or semi-automatically; in this context semi-automaticsampling can imply that the actual sample is taken automatically whilethe probes are changed manually. The sampling devices may, for instance,be of the kind described in SE-B-446,775. Since a given period of timemust lapse in order to enable the melt already present in theconditioning furnace to mix with each new batch of molten iron addedthereto before melt taken from the furnace is able to provide ananalysis result which is representative of the furnace contents, it isnecessary to allow a few moulds, generally about 4-5 moulds, to passbefore a sample is taken after each refilling of the conditioningfurnace. On the other hand, in case of embodiment A, it is necessary tosample at a rate which is sufficiently rapid to ensure that the analysisresult can be used to modify the next base treatment process. Whendetermining the duration of this mixing time, the important parametersthat must be taken into consideration include the length of time takento fill the casting moulds, the volumetric capacity of the moulds, thesize of the conditioning furnace and, where applicable, the size of theladle in which the base treatment is carried out.

The procedures taken when starting up the process are to a large partdependent on the initial conditions: The plant may have been used toproduce gray or ductile iron prior to starting up the process forinstance, or the conditioning furnace may be more or less filled withmelt. Whichever the case may be, the conditioning furnace is firstfilled with molten cast iron, optionally base treated with Mg, until thesulphur and/or additive concentrations of the melt lie essentially inthe correct ranges for the production of CGI. The furnace is filledgenerally on the basis of experience, optionally together with the aidof chemical analysis of samples taken in the spout.

According to embodiment A, at start-up the furnace is filled to roughlythree-quarters of its capacity, after which melt is tapped-off until astable and uniform level of inoculating agent is obtained, this levelgenerally corresponding to about 2-4 casting moulds, whereafter castingis interrupted temporarily and a thermal analysis sample is taken. Theresult of this analysis influences the base treatment of the next batchof melt in the reaction vessel, this melt later filling up theconditioning furnace, and also indicates the possible need to add Mg tothe melt in the conditioning furnace to quickly adjust the system,whereafter production can be started. In the case of planned orundesirable stoppages in operation, the pressure in the furnace isreduced, after having stopped the production, so that melt in thefurnace spout will be drawn back into the furnace and therewith lowerthe fading or oxidation of Mg. Since the fading rate per unit of time inthe furnace is known, it is possible to calculate the reduction inactive Mg during the stoppage period. A corresponding amount of Mg canthen be added to the melt after the stoppage, and production thenrestarted.

The start-up and shut-down procedures are essentially the same asindicated above, where applicable, when practicing embodiment B. Theladles should be preheated. In the case of stoppages, the ladles shouldbe emptied, if possible into moulds but otherwise back into theconditioning furnace within a few minutes after the stop, and, in caseof any longer stop, be reheated; when restarting the production, theladles are simply filled again.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive method will now be described in more detail with referenceto a number of examples and also with reference to the accompanyingdrawings, in which like reference numerals indicate like objects.

FIG. 1 is a principle schematic overview of embodiment A of the methodaccording to the present invention;

FIG. 2 is an example of a control diagram by means of which the contentof graphite shape modifying agents in the melt is controlled whileperforming the method according to FIG. 1;

FIG. 3 is an example of a control diagram similar to the diagram of FIG.2 but concerning the amount of inoculating agent in the melt.

FIG. 4 is a principle schematic overview of embodiment B of the methodaccording to the present invention;

DETAILED DESCRIPTION

In the case of the embodiment illustrated in FIG. 1, which is an exampleof the previously described embodiment A, there is first prepared aniron melt 1 in a furnace 2. In this case, the melt is produced from ironscrap. The C.E. of the melt is adjusted in the furnace 2 by addingcarbon and/or silicon and/or steel to the melt, as indicated at 25. Themelt is then transferred to a ladle 3, in which the melt is subjected toa base treatment process, consisting of the addition of Mg 11 in somesuitable form. Subsequent to this base treatment, slag is removed fromthe melt surface and the melt is transported to and introduced into aclosed conditioning furnace 4, in which a pressurized inert gasatmosphere is maintained and which is of the so-called pressure pouringtype sold by the company ABB under the trademark PRESSPOUR®. Melt istapped from the furnace in a controlled fashion, either by controllingthe gas overpressure in the furnace space 16--with the aid of a slidevalve 17 on the gas delivery line 18--or with the aid of a stopper rod12 which fits into the tapping hole 13 in the spout 9, or by acombination of these control methods. The melt 5 is heated by means ofan induction heating unit 22 and is therewith also remixed to someextent. The batch of melt introduced into the conditioning furnace 4 ismixed with the melt 5 already present therein. About 75% of the maximumcapacity of the furnace is utilized when the process is continuous.Further Mg may be supplied to the furnace 4 when necessary. The Mg issupplied in the form of steel-sheathed Mg-cored wire or rod 6, which isfed into the furnace 4 through a closable opening 7 provided in thefurnace casing 8. As with other additions, the Mg-addition is alsogoverned by the result of the thermal analysis of the cast CGI. Theopening 7 is provided with a slide valve or lid 19. The arrangement alsoincludes a chimney 20 (that optionally may be identical with the opening7) through which particulate MgO, Mg-vapour, and other gases within thefurnace environment are ventilated and which is provided with a slidevalve or lid 21 mounted in the casing 8. The valve 17 is open forcontinuous gas delivery during operation, whereas the valves 19 and 21are closed. When needing to introduce the Mg-wire 6 into the furnace,the furnace pressure is first lowered resulting in level of melt in thespout 9 falling to the level shown in broken lines. This operation takesabout 10-20 seconds to effect. The valve 21 in the chimney 20 and the Mginfeed valve 19 are then opened, which takes about 5 seconds. Mg-coredwire 6 is fed for about 30 seconds into the furnace. The valves 19 and21 are then closed, which takes a further 5 seconds. Finally, the valve17 is opened and the pressure is increased to its normal operatinglevel, which takes about 20 seconds. The time taken to feed Mg-rod 6into the conditioning furnace is thus about 70 seconds in total.Inoculating agent 10 is delivered to the spout 9 of the furnace inaccordance with the aforesaid regulating principle immediately prior totapping-off the melt.

Tapping of melt from the furnace 4 is controlled with the aid of thestopper rod 12. The method sequence is terminated by taking a sample 14for thermal analysis with the aid of a sampling device 23, not describedin detail here. In the illustrated case, the sample is taken in thepouring basin or sprue system 15 of a casting mould 14. In order toensure that the analysis result will represent the contents of thefurnace, 4-5 casting moulds are allowed to pass after each replenishmentof the conditioning furnace, before taking a sample. The sample isanalyzed with the aid of a computer 24, not described in detail here;the broken line arrows indicate the flow of information to and from thecomputer 24.

The additions of graphite shape modifying agents to the system areregulated suitably in accordance with the principles described below,wherein reference is made to the control diagram in FIG. 2 in which thecontrol value for the content of graphite shape modifying agent isplotted on the y-axis as a function of time, which is plotted on thex-axis. The positive values of the y-coordinate indicate excesses inrelation to the control value of graphite shape modifying agent, whilethe negative values indicate a deficiency. The control value coincideswith the x-axis, i.e. when y=0. The reference signs have the followingsignificance:

100=upper specification limit

110=upper control limit

120=lower control limit

130=lower specification limit

When the actual value lies within the control limits (i.e. between thelines 110 and 120) and the trend does not point away from this area, nochange is made to the Mg-addition; the same amount of Mg is included inthe next base treatment process as in the preceding process. If theactual value lies above the upper control limit 110, but below the upperspecification limit 100, the Mg-addition is decreased in the next basetreatment process. If the actual value lies in the corresponding lowerrange (between the lines 120 and 130), the Mg-addition is increased inthe next base treatment process. If the actual value lies above theupper specification limit 100, no more melt is tapped from theconditioning furnace until the Mg-content has faded (intentional), orthe furnace melt is diluted with a melt with a lower Mg-content untilthe Mg-content has reached an acceptable level. A scrap warning is givenat the same time. If the conditioning furnace is not full to capacity, acharge containing less Mg can be added to the existing melt. Tapping ofmelt from the furnace is also interrupted when the actual value fallsbeneath the lower specification limit 130, although in this case Mg-wireis fed to the furnace, while issuing a scrap warning.

The addition of inoculating agent to the melt is controlled in a similarway. The reference signs in FIG. 3 have the same significance as thosein FIG. 2. If the actual value lies within the control limits (betweenthe lines 110 and 120) and the trend does not point away from this area,no change is made to the amount of inoculating agent added to thesystem. If the actual value lies outside the control limits, the amountof inoculating agent added to the melt in the spout of the conditioningfurnace is either increased or decreased; a scrap warning is also issuedwhen the actual value lies outside the specification limits (the lines100 and 130 respectively).

In the case of the embodiment illustrated in FIG. 4, which is an exampleof previously described embodiment B, an iron melt is prepared in afurnace 42. The melt is then transferred to a vessel 43, in which themelt is desulphurized, according to any suitable known process, to aweight percentage of about 0.005-0.01% S. Simultaneously, carbon isadded to a weight percentage of about 3.7% C. in order to adjust theC.E.-value of the melt. Subsequent to this, slag is removed from themelt surface and the melt is transported to and introduced into apressurized conditioning furnace 44 (similar to the furnace 4 in theembodiment A example), having a capacity of about 6 to 65 tons, fromwhich melt is tapped in a controlled manner according to any of themethods indicated in the embodiment A example. The batch of meltintroduced into the conditioning furnace 44 is mixed with the melt 45already present therein, while optional alloying agents, e.g. Cu or Sn,may also be added; such alloying agents may also, or alternatively, beadded at some other suitable point of the process. From the conditiongfurnace, the molten iron is poured into a small treatment or pouringladle 60. The melt in these ladles is then treated with Mg-cored wire 46and inoculating agent 50 immediately prior to casting in moulds 54. Themethod sequence is terminated by taking a thermal analysis sample 63from the ladle 60 or from the pouring basin or sprue system 55 ofcasting moulds 54. As with other additions, the additions of Mg as wellas of inoculation agent are governed by the result of the thermalanalysis of the cast CGI. The control and regulating principlesdescribed in connection with FIG. 2 and 3 are essentially applicablealso in the case of this latter embodiment.

It will be understood that the invention is not restricted to thedescribed and illustrated exemplifying embodiments thereof and that thedescribed method can be modified in many ways within the scope of theinvention and within the expertise of the person skilled in this art.For instance, an additional thermal analysis sampling may be carried outfollowing the optional base treatment, in order to secure an acceptablequality of the feed to the conditioning furnace. Other methodprinciples, devices, components, agents, etc. than indicated above mayof course also be used within the scope of the present invention.

We claim:
 1. A method for continuously providing pre-treated molten ironfor casting objects which solidify as compacted graphite iron,comprising the steps of:(a) continuously producing a succession ofbatches of desulfurized molten cast iron, thereby providing a feedstockthereof; (b) transferring increments of said feedstock of desulfurizedmolten cast iron one after another to a conditioning furnace andintermittently dispensing desulfurized molten cast iron from saidconditioning furnace into a succession of individual casting molds, saidtransferring being conducted so as to maintain the quantity ofdesulfurized molten cast iron in said conditioning furnace withinpredetermined limits, despite said dispensing; (c) periodically taking asample of desulfurized molten cast iron from a respective selected oneof said individual casting molds into a container and allowing thesample to solidify to cast iron from a state in which the sample and thecontainer are substantially in thermal equilibrium at a temperatureabove the crystallization temperature of the sample; (d) while allowingeach sample to solidify to cast iron, recording time-dependenttemperature changes of the sample and using the resulting recordedchanges for establishing structural properties and carbon equivalent ofthe cast iron; (e) comparing the structural properties and carbonequivalent established in each practice of step (d), with knownstructural properties and carbon equivalent equating to acceptablecompacted graphic iron; and (f) upon determining as a result of apractice of step (e) that the established structural properties and/orcarbon equivalent of the cast iron from a respective sample deviate fromthe respective said known structural properties and carbon equivalent bymore than given respective predetermined amounts, practicing at leastone of:(i) adjusting the carbon equivalent of a batch or increment ofsaid feedstock, by adding at least one of carbon, silicon and steelthereto; (ii) adding a correspondingly varied amount of at least onegraphite shape-modifying agent to said desulfurized molten cast iron, inrelation to an amount of graphite shape-modifying agent added to arespective preceding batch or increment and/or in at a precedingincident of addition, by making a corresponding adjustment of additionthereof to at least one of said batch, said increment and saidconditioning furnace; and (iii) adding a correspondingly varied amountof at least one inoculating agent to said conditioning furnaceimmediately prior to pouring desulfurized molten cast iron therefrominto a respective said individual casting mold in a respective practiceof step (b).
 2. The method of claim 1, comprising:practicing step(f)(ii) on respective batches of said desulfurized molten cast iron in areaction vessel; and transferring said batches from said reactionvessel.
 3. The method of claim 1, further comprising:maintaining saidconditioning furnace substantially closed except when transferringdesulfurized molten cast iron thereto or therefrom and when addinggraphite shape-modifying agent or inoculating agent thereto.
 4. Themethod of claim 3, further comprising:providing said conditioningfurnace with a protective internal atmosphere of inert gas.
 5. Themethod of claim 3, further comprising:internally pressuring saidconditioning furnace.
 6. The method of claim 5, furthercomprising:reducing internal pressurization of said conditioning furnacewhen adding graphite shape-modifying agents thereto.
 7. The method ofclaim 1, wherein:each respective selected one of said individual castingmolds has a gate or sprue system, and, in practicing step (c), each saidsample is taken from a respective gate or sprue system.
 8. A method forcontinuously providing pre-treated molten iron for casting objects whichsolidify as compacted graphite iron, comprising the steps of:(a)continuously producing a succession of batches of desulfurized moltencast iron, thereby providing a feedstock thereof; (b) transferringincrements of said feedstock of desulfurized molten cast iron one afteranother to a conditioning furnace, intermittently dispensingdesulfurized molten cast iron from said conditioning furnace into atleast one ladle, and pouring desulfurized molten cast iron from said atleast one ladle into a succession of individual casting molds, saidtransferring being conducted so as to maintain the quantity ofdesulfurized molten cast iron in said conditioning furnace withinpredetermined limits, despite said dispensing; (c) periodically taking asample of desulfurized molten cast iron from a respective selected oneof said individual casting molds into a container and allowing thesample to solidify to cast iron from a state in which the sample and thecontainer are substantially in thermal equilibrium at a temperatureabove the crystallization temperature of the sample; (d) while allowingeach sample to solidify to cast iron, recording time-dependenttemperature changes of the sample and using the resulting recordedchanges for establishing structural properties and carbon equivalent ofthe cast iron; (e) comparing the structural properties and carbonequivalent established in each practice of step (d), with knownstructural properties and carbon equivalent equating to acceptablecompacted graphic iron; and (f) upon determining as a result of apractice of step (e) that the established structural properties and/orcarbon equivalent of the cast iron from a respective sample deviate fromthe respective said known structural properties and carbon equivalent bymore than given respective predetermined amounts, practicing at leastone of:(i) adjusting the carbon equivalent of a batch or increment ofsaid feedstock, by adding at least one of carbon, silicon and steelthereto; (ii) adding a correspondingly varied amount of at least onegraphite shape-modifying agent to said desulfurized molten cast iron, inrelation to an amount of graphite shape-modifying agent added to arespective preceding ladle of said feedstock, by making a correspondingadjustment of addition thereof to a respective said ladle; and (iii)adding a correspondingly varied amount of at least one inoculating agentto a respective said ladle prior to pouring desulfurized molten castiron therefrom into a respective said individual casting mold in arespective practice of step (b).
 9. The method of claim 8, furthercomprising:maintaining said conditioning furnace substantially closedexcept when transferring desulfurized molten cast iron thereto ortherefrom and when adding graphite shape-modifying agent or inoculatingagent thereto.
 10. The method of claim 9, further comprising:providingsaid conditioning furnace with a protective internal atmosphere of inertgas.
 11. The method of claim 9, further comprising:internallypressurizing said conditioning furnace.
 12. The method of claim 8,wherein:each respective selected one of said individual casting moldshas a gate or sprue system, and, in practicing step (c), each saidsample is taken from a respective gate or sprue system.